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Velarian

VVT pot characteristics questions

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Posted (edited)

I have a MIJ Jazz Bass (‘62 Reissue) and the the way the volume and the tone pots work doesn’t seem right to me. They’re marked A250k. I’d be grateful for any views on what is ‘normal’ and any possible solutions if what I’m about to describe isn’t normal. There are two main issues: -

  1. Starting from full volume, the volume pots are OK when turning down for about the first 15-20% of travel and then they drop off rapidly so there is very little fine control of the volume of each pickup.
  2. The tone control behaves similarly but it doesn’t actually cut the top end very much and it acts more like a volume control. It has a 0.047uF capacitor (marked 473k) which I would have thought would darken the tone quite a bit but it’s still relatively bright but at a much lower volume. 

I’ve done some reading on how pots work and from what I’ve found, the rapid drop-off of volume sounds a bit like a 'Commercial log' taper and I wondered if this was trying to recreate the characteristics of Vintage ‘62 instrument?

So, my question is, should I do anything about it? If so is there anything I can do short of replacing the whole wiring loom?

Edited by Velarian
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6 minutes ago, nilebodgers said:

Note that there are different audio tapers too - e.g. https://www.axesrus.co.uk/CTS-Pots-Solid-Shaft-p/cts63.htm there is a “vintage” and “modern” audio taper that will affect how volume varies with pot rotation. (There are actually other variations, but they aren’t commonly available, at least in the uk)

 

Thanks for the link, looks interesting. I’ll give it a read in the morning when I’m more likely to understand it 😄

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The picture tells something I particularly hate: no soldered earth to the jack. Cheapo. I would never rely on the plate ground only.

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7 hours ago, itu said:

The picture tells something I particularly hate: no soldered earth to the jack. Cheapo. I would never rely on the plate ground only.

Thanks for pointing that out, I wouldn’t have known!

 I’m thinking it might just be easier to replace the whole lot now. 

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I hate that plate ground thing too. I think it actually is period-correct, but it is still rubbish.

I’d certainly swap those mini pots for full size CTS if I was reworking it. (The plate holes will need drilling out to take full-size pots though.)

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If you want to be able to use your controls all along their curve, excursion or rotation (or whatever you want to call it), use linear potentiometers.

If you want that on/off thing use logarithmic potentiometers.

And like the others I hate this plate grounding.

That said a single ground point, called star grounding, is the best way to do it, avoiding ground loops (which is one of the typical basic Fender bass or guitar noise issue).

I'd like to add that mixing two pickups precisely with logarithmic volume potentiometers is close to a nightmare...

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3 hours ago, nilebodgers said:

I hate that plate ground thing too. I think it actually is period-correct, but it is still rubbish.

I’d certainly swap those mini pots for full size CTS if I was reworking it. (The plate holes will need drilling out to take full-size pots though.)

Thanks, I think that’s what I’ll do. A straight swap with one of @KiOgon‘s replacement looms looks like the way to go.

 Good point about the holes in the plate, cheers. 

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1 hour ago, Hellzero said:

If you want to be able to use your controls all along their curve, excursion or rotation (or whatever you want to call it), use linear potentiometers.

If you want that on/off thing use logarithmic potentiometers.

And like the others I hate this plate grounding.

That said a single ground point, called star grounding, is the best way to do it, avoiding ground loops (which is one of the typical basic Fender bass or guitar noise issue).

I'd like to add that mixing two pickups precisely with logarithmic volume potentiometers is close to a nightmare...

Thanks, would a volume + blend control rather than two separate volumes work better do you think?

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Posted (edited)

If you want precise adjustments, yes. If each pot is always full on, then no.

And take an MN type blend, so there won't be any loss when both pickups are "centered".

d863f7eca98495df3d1ccb99c5f2028ea0b06202

Edited by Hellzero
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41 minutes ago, Hellzero said:

If you want precise adjustments, yes. If each pot is always full on, then no.

And take an MN type blend, so there won't be any loss when both pickups are "centered".

d863f7eca98495df3d1ccb99c5f2028ea0b06202

Thanks for that. 

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Posted (edited)

Got a Bourns MN from WD Guitars to replace the AC blend in my Ibanez SR600.

https://www.wdmusic.co.uk/electronics-c17/pots-c69

Check the mounting bush dia if ya got mini pots... had to open up the mounting hole a couple of mm with a tapered reamer.

Oh, and KiOgon is a top bloke and very helpful with wiring questions, i would of got the pots of him, but he didn't have the MN in plain shaft...

Edited by PaulThePlug

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I’ve ordered a replacement wiring loom from @KiOgon which has Bourns mini pots. The mounting hole size is, as pointed out, a couple of mm too small on my existing control plate so I’ve got my tapered reamer standing by to take care of it. 🙂

 Thanks everyone for all the replies. I’ll report back when everything is hooked up and tested. 

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39 minutes ago, Velarian said:

I’ve ordered a replacement wiring loom from @KiOgon which has Bourns mini pots. The mounting hole size is, as pointed out, a couple of mm too small on my existing control plate so I’ve got my tapered reamer standing by to take care of it. 🙂

 Thanks everyone for all the replies. I’ll report back when everything is hooked up and tested. 

@KiOgon has done a 3 looms for me. 2 where there was a master volume, blend and tone (For a Jazz Bass). Easy to install and pretty much foolproof to use. Plus he never got angry at me for asking a huge amount of questions. Top guy. The loom should be killer. 

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Posted (edited)
On 01/06/2021 at 22:31, itu said:

https://eepower.com/resistor-guide/resistor-types/potentiometer-taper/

Here A should mean Audio i.e. logarithmic. Are the electronics modded or changed in any way (picture, please)?

Be careful, although A denotes Audio* in American, it was always B in the UK. I usually use either OMEG or Alpha pots and the OMEGs use the British convention and the Alphas the US convention. Incidently, there is nothing special about CTS pots, they were easy to obtain for Leo so he used them, the same goes for the woods he used on his instruments. All native North American  species.

I recently fitted some DiMarzios to my Aerodyne PJ and used their wiring diagrams, as advised by their tech team. They use logarithmic pots and seem to give more control than on any passive bass I have had before. YMMV

*Audio Taper is really a logarithmic or log pot.

Edited by Chienmortbb

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4 hours ago, Chienmortbb said:

Be careful, although A denotes Audio* in American...

Dear Sir, if you read the article in the link...

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Fender used the controls-plate for chassis Ground for a very very long time & it worked just fine.

Have there been studies that show a Mechanical Ground isn't as good as a soldered Ground?, I doubt it...

 

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10 minutes ago, Killed_by_Death said:

 

Fender used the controls-plate for chassis Ground for a very very long time & it worked just fine.

Have there been studies that show a Mechanical Ground isn't as good as a soldered Ground?, I doubt it...

 

nope, but I once had a pedal where the sockets were 'grounded' via their physical contact with the case. It worked fine until the socket worked loose, and I lost my signal. 

If it can happen there, then it can happen on a bass, so I'd rather not take the chance.

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6 minutes ago, Killed_by_Death said:

Fender used the controls-plate for chassis Ground for a very very long time & it worked just fine.

Why not, everything else is also cheap in Fenders. That was Leo's intention in the first place: not a through-neck, one simple pickup etc.

Relying to a single screw it is possible to save some tin, too. But reliable that connection is not.

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I have a strong aversion to people soldering a Capacitor between two pots, straddling them. It's almost irrational, but there is a reason.

o9uo7qjc1dvcz9vcvspr.jpg

but the inherent Ground provided by the Mechanical connection to the controls-plate never bothered me

Fender used discarded floor tiles for inlays, in the early days.

 

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16 hours ago, paul_5 said:

I once had a pedal where the sockets were 'grounded' via their physical contact with the case. It worked fine until the socket worked loose, and I lost my signal. 

I like a personal anecdote for reasoning & it drives me bonkers when I use a personal anecdote that is summarily ignored by the naysayers.

 

16 hours ago, itu said:

reliable that connection is not

Even when the jack is tightened into the controls-platre properly?

 

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Never had a car that doesn't start because of this stupid chassis grounding only that has rusted or got loose ?

Now you have a non anecdotal explanation and you know why modern cars have multiple chassis groundings.

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